A. Field of the Invention
The present invention relates generally to the field of biology. More particularly, it concerns fertility assays and associated compositions.
B. Description of Related Art
An estimated 20-25% of couples currently seeking infertility treatment are diagnosed with idiopathic or unexplained infertility, where approximately half of those cases are due to male infertility. While many diagnostic options have been developed to evaluate female infertility, male infertility lacks a truly objective semen assay capable of detecting a wide array of both visible and cryptic sperm abnormalities. Consequently, there is a great demand for an accurate and objective means of semen analysis (Amann, 1989) that would be superior to the useful, yet somewhat limited subjective techniques based on strict morphology standards (Kruger et al., 1987; WHO, 1987, 1992, 1999).
The evaluation of sperm motility and morphology as an indicator of infertility has significant limitations (Eliasson, 2003). Automated semen analyses such as CASA and IVOS (Douglas-Hamilton, 1995; Krause, 1995) have been developed for clinical use based on measurements of sperm motility and morphology. Motility is, however, a variable sperm characteristic that declines rapidly after sample donation and depends largely on the length of time between collection and evaluation (typically up to 2 hours post collection; Drobnis, 1992, Eliason, 1981, Jorgensen et al., 1997). While there is a significant overlap between semen parameters of fertile and infertile men, sperm morphology is thought to be a stronger infertility predictor than sperm motility (Guzick et al., 2001).
Other techniques also have significant limitations for evaluation of male fertility. Membrane permeant nuclear stains (Garner and Thomas, 1999) and vital mitochondrial dyes (Evenson et al., 1982; Garner and Thomas, 1999) may be used to discriminate between live and dead spermatozoa. Terminal deoxynucleotidyl transferase-mediated, dUTP nick-end labeling (TUNEL), ELISA or Comet assays are suggestive of the apoptotic or necrotic process in spermatozoa and can be used to screen for DNA strand breaks in some defective spermatozoa (Baccetti et al., 1996; Hughes et al., 1999; Sun et al., 1997; van der Schans et al., 2000). DNA-specific dyes applied to intact (Ferrari et al., 1998) or denatured (SCSA; Ballachey et al., 1987) bull sperm correlate with fertility, but may not correlate well with the results of microscopic semen analysis (Evenson et al., 1999). Chromatin-based assays provide useful information about sperm quality, though they may not cover the whole spectrum of sperm head and tail abnormalities found in both fertile and subfertile semen samples (Sutovsky et al., 2001b; 2002). Thus, a need exists for the creation of an accurate and objective means of semen analysis.